1. Field of the Invention
This invention relates in general to a method and apparatus for detecting leaks in fuel dispensing systems utilizing underground storage tanks, and in particular to a valve and pressure monitoring system for isolating the flow line leading to the dispenser from the remaining portions of the control housing for the submersible pump system.
2. Description of the Prior Art
Gasoline stations utilize underground storage tanks for containing gasoline and diesel fuel. A submersible pump will by submersed in the fuel tank. Conduit leads from the pump to a control housing mounted above the fuel tank, but still below the ground. The control housing contains a number of elements for controlling the pumping of the fuel. A check valve is part of these elements. The check valve separates an inlet chamber in the housing from an outlet chamber. The outlet chamber leads to a flow line, which leads to the dispensing unit on the surface.
When dispensing fuel, the dispenser will turn the pump on. The pump will apply a pressure of about 30 PSI to the control housing and flow line. When the pump turns off, the check valve closes. The check valve will cause the line pressure to bleed off to about 6-12 PSI. If it bleeds off any more than that, there will be a malfunction or leak in the system. The leak could be from a malfunction in the check valve, the siphon valve, the functional element or from other portions of the control housing. Or, there could be a leak in the flow line leading to the dispenser.
Some control housings have leak detectors mounted to them. The leak detector mounts in a receptacle located in the outlet chamber of the control housing downstream from the check valve. The leak detector is a pressure monitoring device. If the pressure in the outlet chamber drops below a minimum level, then it will provide a signal to disable the system from further operation until the leak is detected.
Determining the location of the leak can be a problem. The leak could be in the flow line, or it could be in the control housing. The prior art leak detector will not indicate where the leak is occurring. This involves replacing parts in some cases that do not need replacing.